The role of environmental light exposure and the biological abnormalities responsible for winter SAD are unknown. We have pursued the ophthalmic pathophysiology of SAD along two lines: light exposure to the eye, and the response of the eye to light. To examine whether patients with SAD inhabited environments with different light exposure from people without SAD, we evaluated ambient light exposure using a light monitor that measured environmental light levels as sensed by the human eye in 13 patients and 13 age- and sex-matched controls. We found no difference between the two groups. To consider the possibility that SAD patients have abnormal intraocular pressures and that this variable may be sensitive to light therapy, we examined intraocular pressure in 14 depressed patients and 14 age- and sex-matched normal controls subjects before and after periods of two weeks in which subjects received light therapy. We found no difference between the two groups or between the two conditions of light therapy. To assess seasonal changes in light sensitivity, we evaluated dark adaptation in winter and summer in 11 medication-free patients and 19 controls. We found no difference between the two groups or across seasons. To replicate a prior report of abnormal electrooculogram ratios in SAD, we measured this variable in 16 patients and 16 age-, sex-, and medication-matched controls before and after one week of light therapy. The mean EOG ratios were significantly lower in patients than in controls. There was no effect of light therapy upon the ratios. We plan to continue our investigation of electrooculographic abnormalities by repeating these studies in patients and volunteers during the summer season. We also plan to study whether pharmacological methods of enhancing light sensitivity in patients with SAD might prove beneficial to patients with this syndrome.